Recently, in line with miniaturization, lightweight, thin profile, and portable trends in electronic devices according to the development of information and telecommunications industry, the need for high energy density batteries used as power sources of such electronic devices has increased. Currently, research into lithium secondary batteries, as batteries that may best satisfy the above need, has actively conducted.
Various types of carbon-based materials including artificial graphite, natural graphite, or hard carbon, which are capable of intercalating/deintercalating lithium, have been used as anode active materials of lithium secondary batteries. Among the carbon-based materials, since graphite provides advantages in terms of energy density of a lithium battery and also guarantees long lifespan of the lithium secondary battery due to excellent reversibility, graphite has been most widely used.
However, since graphite may have a low capacity in terms of energy density per unit volume of an electrode and may facilitate side reactions with an organic electrolyte at a high discharge voltage, there is a risk of fire or explosion due to malfunction and overcharge of the battery.
Thus, metal-based anode active materials, such as silicon (Si), have been studied. It is known that a Si metal-based anode active material exhibits a high lithium capacity of about 4,200 mAh/g. However, the Si metal-based anode active material may cause a volumetric change of a maximum of 300% or more before and after the reaction with lithium, i.e., during charge and discharge. As a result, conductive networks in the electrode are damaged and contact resistance between particles is increased. Thus, there is a phenomenon in which a battery performance degrades.
Thus, a method of reducing substantial variations in diameter according to the volumetric change by reducing the size of silicon particles to a nano size has been attempted. However, there are difficulties in developing a method of synthesizing a uniform nano-silicon anode active material and uniformly distributing the nano-silicon anode active material in a slurry, and side reactions with an electrolyte may increase because a surface area is maximized.
Therefore, there is a need to develop an anode active material which may replace a typical anode active material and may address limitations in the side reactions with an electrolyte, volume expansion during charge and discharge, and performance degradation of a secondary battery.